Developing electrostatic charge image with a liquid developer of two immiscible phases



DEVELOPING ELECTROSTATIC CHARGE IMAGE WITH A LIQUID DEVELOPER OF TWO IMMISCIBLE PHASES 2 Sheets-Sheet 1 Filed Sept. 23. 1958 H 4 KA 2 o w/ w 4/, P B N4 u 7 2L N m) 1 m G F j P -*DEVELOPER FLOW DEVELOPER FLOW FIG-4 FIG-6 FIG-7 INVENTORS DONALD L. FAUSER 8x Y EDWIN R. KOLB ATTORNEYS March 1967 I D. FAUSER ETA DEVELOPING ELECTROSTATIC CHARGE IMAGE WITH A LIQUID DEVELOPER OF TWO IMMISCIBLE FHASES Filed Sept. 23, 1958 2 Sheets-Sheet 2 INVENTORS DONALD L. FAUSER a BY sowm R. KOLB wum, M, ea

ATTORNEYS DEVELOPING ELECTROSTATIC CHARGE IMAGE WITH A LIQUKD DEVELOPER OF TWO IMMIS- CIBLE PHASES Donald L. Fauser, Lakewood, and Edwin R. Kolb, Grafton, Ohio, assignors to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Filed Sept. 23, 1958, Ser. No. 762,756 9 Claims. (Cl. 117-37) This invention relates to electrophotography and, more particularly, to improved systems for developing and fixing latent electrostatic images using liquid development techniques and compositions.

Electrophotographic or electrostatic reproduction processes of the character to which this invention relates include processes such as are disclosed in the copending application of Dolar N. Adams and Donald L. Fauser, Ser. No. 640,353, filed Feb. 15, 1957, and comprise generally the steps of impressing an electrostatic charge on a plate or paper or other image carrier base or sheet having an electrophotographic or electrophotosensitive surface, exposing the charged surface to a light image whereby portions of the charged surface corresponding to the light image are discharged to form an electrostatic image or pattern, and rendering the electrostatic pattern visible or developed by applying thereto a visible developing agent or other developing agent having electrostatic charge characteristics such that it will be attracted to the charged areas and not to the discharged areas of the exposed surface, or vice'versa, and then fixing the developing agent more or less permanently in place as electrostatically deposited to form the image.

It should be noted that, in the following description and claims, such expressions as developed, developer, development, etc., should be understood as not necessarily being restricted to the rendering of a latent or electrostatic image visible to the eye, as such terms are generally understood in discussions of, for example, silver halide photography. Thus, in the development or rendering useful of an electrostatic image on, for example, a printing plate for lithographic printing, whether or not the image is developed so as to be rendered visible to the eye is not nearly so important as whether or not the image is developed in such manner as to have the correct oleophilic ink-receptive surface characteristics for the lithographic process, and such can be achieved, according to this invention, using as a developer a perfectly clear resin which, when dried and fixed to the plate, has little or no visible contrast with background or non-image areas of the plate. Similarly, in the production of, for example, a printed electric circuit, whether or not the developed image is visible is not as important as whether or not it is in a condition to be resistant to an etching composition or receptive to an etch-resistant paint or coating. Accordingly, the following description and claims should be read and understood as meaning, whenever reference is made to a developer or to developing, etc., not only rendering a latent electrostatic image visible to the eye as in the usual meaning of these terms, but also the broader connotation of rendering a latent electro static image permanent or useful for whatever use is desired for it.

Generally, as will be understood, the final visual definition, resolution, continuity, and contrast (or the equivalent non-visual counterparts of those characteristics as noted in the preceding paragraph) of the ultimate developed image obtained by such electrophotographic processes are, in large measure, a function of the fineness, uniformity, and control with which a developing agent is or may be applied to the latent or invisible electrostatic image which, in most cases, is believed to possess inherent definition, clarity, and fineness to a degree exceeding that obtainable by either chemically photosensitive systems as heretofore known or development techniques for electrophotography previously utilized.

Thus, if the developing agent is in the form of a fusible resin powder in conjunction with a carrier material having appropriate electrostatic characteristics (such as glass beads or iron filings, etc.), the fineness and definition of,

the resultant image (somewhat comparable to the socalled grain of conventional silver halide or other chemically photosensitive photographic systems) may be interrupted or determined by the minimum fineness of the developer or the carrier particles required by the electrostatic arrangements. Similarly, if a so-called powder cloud developing system is used whereby developer particles are suspended in air or other gaseous fluid, the ultimate product may be disadvantageously affected by the aerodynamic requirement of the developing system, as well as interjecting, in addition to the aforementioned disadvantages, the possibility that desirably fine particle size may lead to difliculties in containing the powder cloud against dissipation from dusting and the further possibility that, with ultra-fine particles suspended in air and each of which is, by definition, charged to the same polarity, optimum electrostatic deposition of the particles on the charged electrostatic image may be interfered with by the electrostatic repulsive forces among the particles themselves.

Similarly, as will be understood, the particular electrostatic characteristics of a developer material required to provide the deposition thereof on the electrostatic image may be (and usually are) quite independent of such characteristics as color or visible contrast with the background, particle fineness, oleophilic and similar surface characteristics, film-forming ability, and similar characteristics having to do with the desired ultimate characteristics of the developed image, as well as being independent of such characteristics of fusibility, solubility, adhesiveness, etc., which may be important or controlling in permanently fixing the developer materials to the image surface after they have once been electrostatically deposited thereon. Also, as will be understood, the foregoing independent,

and, perhaps, actually inconsistent or disparate, characteristics may all, similarly, be independent of the purely mechanical characteristics of the developer material when considered in mechanically cascading, aerodynamic, or

hydrodynamic systems of appplication.

According to this invention, however, liquid developing systems for such electrophotographic processes are provided whereby the developing agent, whether initially or ultimately itself in a liquid or solid form, is applied to the charged image in a liquid composition, particularly as finely divided particles or droplets dispersed in a non-conductive liquid medium for enhancing the formative application, finer resolution and clarity, better control of intensity, and greater freedom of choice of materials to provide the desired color or intensity or other visible or chemical or mechanical characteristics in the ultimate developed image. This invention also includes the provisions of characteristics or components in the developing agent whereby more or less permanent fixing of the developer onto the image is obtained after the electrostatic deposition thereon, and. has, as a further advantage, the utilization of counter-electrode means whereby an enhanced control of the intensity and uniformity of electrostatic deposition of the developer material is obtained.

One object of this invention is to provide liquid developing compositions of the character described for application to the surface of charge electrophotographic image carrier to render visible or otherwise useful an electrostatic image thereon and including components 3 whereby such visible or useful image may be rendered essentially permanent or fixed or non-smudging.

Another object of this invention is to provide liquid developing compositions of the character described for use with electrophotographic or electrostatic reproduction techniques and including a pigment component and a binder component for fixing said pigment in position on an electrostatic image, both said components being finely and uniformly dispersed in an electrically nonconductive liquid vehicle.

A further object of this invention is to provide methods of the character described for the liquid development of electrostatic patterns or images in elec'trophotography to render said images visible or otherwise useful and using for such development particles or droplets of a developing agent dispersedin a non-conducting liquid vehicle therefor and adapted to be electrostatically precipitated from said vehicle onto said image.

, Still another object of this invention is to provide liquid developer systems for the development of latent electrostatic images in electrophotography whereby finely divided charged particles or droplets of developer material are electrostatically precipitated from a liquid vehicle or carrier in which they are dispersed and are thereafter substantially permanently fixed to the surface of the image.

A still further object of this invention is to provide liquid developing compositions of the character described for use with electrophotographic or electrostatic reproduction techniques and including a resin developing material, with or Without a dye or pigment for controlling the visible color or intensity of the resin, dispersed in finely divided form in a substantially non-conducting liquid vehicle or carrier which has substantially no solvent or softening action on the electrostatic image film being developed, and including provision for the substantially permanently fixing of the developer material onto the surface of the electrostatic image on which it is electrostatically deposited during development.

Still another object of this invention is to provide, in electrophotographic reproduction processes of the character described, av system for the liquid development of an electrostatic image on an electrophotosensitive surface whereby the electrophotosensitive surface and the liquid developing material are specifically selected to have components or characteristics adapted, after development of the image by electrostatic deposition thereupon of a developer agent from the liquid developer material, for co-action to fix the developer agent more or less permanently onto those areas of the image surface on which it was electrostatically deposited.

A still further object of this invention is to provide apparatus for continuous electrophotographic reproduction of images on a web of electrophotosensitive sheet materials such as paper and the like and including provision for the liquid development of such images reproduced thereon.

Still another object of this invention is to provide, in the liquid development systems of the character described, means and compositions whereby an electric field is formed outwardly of the charged image surface being developed and the liquid developer is flowed through such field for electrostatic precipitation and deposition on the image surface in charged areas of the field of finely divided developer materials dispersed in the liquid medium.

Other objects and advantages will be apparent from the following description and the appended claims.

It will be understood that, in electrostatic or electrophotographic reproducing techniques of the character to which this invention relates, an electrophotosensitive film is provided on the surface of a sheet of paper or plate or other image carrier base on which an image is to be produced. -As noted, the image may ultimately be desired to be visible (as with the photographic reproduction of pictures or written matter) or have other particular characteristics as utility (as the oleophilic nature desired for an image on a lithographic printing plate) or be textured, electrically conductive or non-conductive, etc. Regardless of Whatever are desired to be final characteristics of the ultimately produced image or pattern, the electrophotographic production thereof indicates that the electrophotosensitive film on the plate or other image carrier is capable of retaining an electrostatic charge, and may include an electrically insulating film-forming and binder component through which is dispersed a photoconductive or photosensitive component capable of lowering or removing an electrostatic charge applied to the electrophotosensitive film but selectively only those areas of the film which are exposed to light.

Considering as illustrative of such electrophotographic processes, the use of a sensitized sheet of paper with an electrophotosensitive film applied to the surface thereof, as more particularly-pointed out in the above mentioned co-pending application. This film, including an insulating or dielectric film-forming component and a photocoductive component as described, is given a uniform negative electrostatic charge in the dark room or otherwise in the absence of light. The charged sheet is then exposed to a light image, as, for example, by projecting an image thereon through a photographic transparency. Where the light strikes the film on the sheet, the original negative electrostatic charge is lowered or removed through the action of the photoconductive component in the film. This leaves an electrostatic latent image or pattern or charge image on the sheet corresponding to the light image projected thereon, but such electrostatic image is, of course, invisible, and the surface characteristics of the sheet, except for an electrostatic charge thereon in selected areas, are substantially unchanged from the original characteristics and/ or relatively as between exposed and unexposed areas thereof.

To render this latent electrostatic image or pattern visible or useful or otherwise to alter the surface characteristics of the film selectively in exposed or unexposed areas (depending upon the final use to which the image is to be put), some sort of developing material or resin or pigment or dye or mixtures thereof is used which can be made to become electrostatically attracted to or repelled by, as the case may be, those areas of the electrostatic image in which the original uniform charge was altered by exposure to light. Advantageously, such developer material may include a binding component which, inherently or upon further treatment such as heating or reaction with after-applied materials, will more or less permanently become afiixed to the desired areas of the image to which the developer is electrostatically attracted or deposited. As will be understood, however, the various unrelated and ultimately desired characteristics of such a developing agent (such as intense color for good visibility, a particular desired color, fineness for good definition, convertibility to a more or less permanently adhering or fixed condition, or the ability to provide final surface characteristics of being oleophilic, etch resistant, electrically conductive, textured, etc.) may not necesarily all inhere in a particular material which also possesses electrostatic characteristics as required for the electrostatic attraction and deposition thereof to the electrostatic image.

As noted, one of the substantial advantages in the utilization of liquid development techniques embodying this invention stems from the relative ease and control obtaining in the use of desirably finely divided developer particles or droplets when they are dispersed in a liquid medium or carrier instead of in a gaseous or mechanical carrier, and fine particle size for-the developer materials appears to have an important effect on the clarity and definition achieved in the developed image and particularly, as will be understood, in the reproduction of continuous tone photographs and multi-color images. Similarly, the application of finely divided developer particles in a liquid carrier or vehicle enhances both the ease of control and the application of a desirably concentrated dispersion, perhaps primarily because the liquid developers are subject to hydrodynamic consideration of flow, etc., and are substantially free of problems incident to aerodynamic application, dusting problems, and the difiiculty of preventing waste or escape of the developer particles of a powder cloud, etc.

Thus, liquid developers according to this invention have satisfactorily been prepared'with the developer material dispersed or emulsified in the vehicle in colloidal particle sizes or droplet sizes providing virtually no settling out or escape of the developer material from the vehicle and yet producing a liquid controllable according to regular hydrodynamic considerations. Especially with the use of a closely spaced counter-electrode, as hereinafter described, substantial advantage obtains by having the developer material in a liquid phase which can be flowed satisfactorily through a very narrow spacing between the image surface and the counter-electrode as noted below.

Perhaps a less obvious advantage in using liquid developer systems according to this invention resides in the fact that, by the appropriate selection of vehicle, the charged developer particles can be presented to the charged surface of the image to be developed in a medium which is substantially entirely non-conducting and dielectric. Thus, the charges and electrostatic considerations involved in such electrophotographic reproduction systems (and particularly those where the image to be produced is a continuous tone picture) may involve rather small charges or differences in charge to which the developer particles must respond. If the development is carried on completely in a medium composed of nonpolar organic solvents (such as gasoline, carbon tetrachloride, kerosene, Varuolene, and the like, having an inherent resistivity of the order of to 10 ohm-centimeters), the medium or atmosphere in whichthe developer particles are to be attracted to the charged image areas may be considered as even more insulating or dielectric than, for example, air with regard to the orders of magnitude of the charges involved. This eifect is, also, enhanced by selecting, according to this invention, such non-polar organic vehicles because, among other reasons, the non-polar characteristics thereof indicate that the high resistivity desired will not be diminished, for example, by the vehicle taking up moisture from the atmosphere.

The particular selection of non-polar organic liquids, according to this invention, as vehicles for the liquid developing compositions also leads to satisfactory use of such compositions with a wide variety of electrophotosensitive image films. Thus, it is known to produce the electrophotosensitive sheet or plate or image carrier by forming on a suitable base a film of a finely divided photoconductive material uniformly dispersed through a resinous binder (for example, as disclosed in the aforementioned copending application) as well as having the initially electrophotosensitive plate surface copolymers, methyl vinyl ether maleic anhydride copolymers, organic acid styrene copolymers, etc.) or they may be soluble only in polar organic solvents (such as certain acrylic acid esters, silicon resins, etc.).

By selecting the developer vehicle according to this invention, then, to be a non-polar organic liquid, in addition to the electrical advantages stemming therefrom, the

further advantages obtain of having a developed composition satisfactorily applicable for use with a wide variety of different image films, none of which is soluble in the non-polar organic developer vehicle. That is, of course, it is not desired to have the liquid vehicle of the developer such that it will distort or dissolve off or otherwise ruin the image film itself when applied thereto during development, and this is particularly true where,

e for reasons of convenience in handling or electrostatic considerations, the sheet or plate or image being developed is completely immersed in the developing material or developer vehicle.

The selection of a specific developer material for electrostatic deposition on the charge image depends somewhat on a Wide variety of conditions and end results desired. Basically, since it is desired according to this invention to present or apply to the charged image surface a finely divided dispersion of developer agent in the non-polar organic liquid from which the developer agent will be precipitated or deposited by electrostatic attraction to the charged image areas, a wide variety of agents may be used provided that they are dispersible (but not soluble) in the non-polar vehicle and may ac quire as dispersed therein an electrostatic charge of the correct polarity for appropriate attraction to the charge on the image surface. Thus, a wide variety of solid inorganic and organic pigments may be selected for dispersion in a non-polar organic vehicle, and particularly where the primary desire of the developing step is merely to render the electrostatic image visible in an appropriate color and with, of course, appropriate fixing of the pigment to the image surface, as described below.

A preferred developer composition, however, involves producing as the liquid developer material an organosol in which a solution of a resin developing agent in a polar solvent therefor which is miscible in the non-polar vehicle is dispersed, preferably in colloidal dimensions, in the non-polar vehicle. As illustrative of such arrangement may be noted organosols of a mesityl oxide solution of saran resin dispersed in Varnolene as the nonpolar vehicle, an isopropenyl acetate solution of Epon resin dispersed in Varnolene, tan isopropenyl acetate solution of polyisopropenyl acetate resin dispersed in Varnolene, a mesityl oxide solution of Epon resin dispersed in the non-polar organic liquid, etc. In this connection, it should be noted that the polarity of the charge acquired by the droplets of resin solution in such an organosol may vary with different resins and, perhaps, different polar solvents therefor. For example, droplets of a mesityl oxide solution of saran resin dispersed as an organosol in Varnolene acquire a negative electrostatic charge, whereas droplets of an isopropenyl acetate solution of Epon resin dispersed as an organosol in Varnolene acquire a positive electrostatic charge. Thus there are available according to this invention properly charged developer materials for use where the image to be developed has either a positive or a negative electrostatic charge.

Since the foregoing resin developer agents, even when deposited on the image surface and fixed thereto as noted below, may not provide the desired visible or colored or other characteristic for the image, a dye material (or a solution of a dye material in a solvent which is the same as or compatible with the resin solvent) may be added to the resin solution, droplets of which are dispersed in the non-polar vehicle. Similarly, inorganic or organic pigments which are not soluble in any of the liquids of the system may satisfactorily be dispersed, for reasons of coloring or otherwise, in the resin-solvent solution, droplets of which form the organosol in the non-polar vehicle. In such case, the actual developing agent to be electrostatically deposited from the vehicle on to the charged image surface includes dyed or pigmented (or both) particles or droplets of resin solution. As noted below, particularly if the resin is a filmforming resin or hinder, this is a highly satisfactory and convenient way of developing the image wit-h various common solid, non-fusible, insoluble pigment materials to a desired degree of intensity or color with the resin serving. to bind the pigment onto the image, thereby greatly aiding in the problem of permanently fixing such common pigments as carbon black, titanium dioxide, zinc oxide, metallic sulphides, and other common colored pigments to the image.

Actually, and particularly related to a developing step which produces a visible image of a particular desired col-or, one convenient commercial source of desirably finely divided colored pigments ground into a binder material is the variety of commercially available printing inks in various colors and consistencies, whether of the variety which binds merely upon the evaporation of solvent (as with a lacquer) or of the oxidizable or dryable variety of binder (as with linseed oil types), which, being essentially polar solvent systems, are satisfactorily dispersed in non-polar vehicles according to this invention to form dyed or pigmented (or both) organosols Withwhich satisfactory results are achieved in the liquid, development of electrostatic images according to this invention. It should also be noted that satisfactory results are achieved with liquid developers according to this invention which include a solution of a dye material (as distinguished. from a resin binder) in a polar solvent with the solution dispersed in the non-polar vehicle. Such a system is illustrated by a dye such as Iosol Black dissolved in, for example, mesityl oxide or isopropenyl acetate and dispersed in Varnolene. The foregoing is also intended to include water solutions of water-soluble dyes dispersed (in a water-in-oil emulsion) in the nonpolar organic liquid.

As will be understood, which of the foregoing particular materials and/or systems is selected will depend in large measure on the final visual and/or physiochemical or other characteristics desired in the final developed image, the uses to which the image and/or the electrophotographic reproduction is to be put, as well as the particular technique of permanently fixing the developing agent to the surface of the developed image. For example, a dispersion of pigment alone in the liquid vehicle with an after application of fixing binder may, for some uses, be perfectly satisfactory. In other instances, it may be convenient to include a resin material which will, itself, during drying of the developed image, permanently fix a dye or pigmented surface to the image. As noted before, the particular visual characteristics of the resultant product may be less important than other surface characteristics thereof, such as, for example, providing as a developing agent a resin material, regardless of its visual characteristics, which will, upon drying and curing, form a desirably oleophilic film for the reception of lithographic ink in the developed image areas.

After the initial electrostatic deposition or precipitation of the various developer agents according to this invention has been achieved on the charged image surface of the image carrier, some means is necessary for the fixing of the deposited material in more or less permanent, non-smudging, or useful condition to provide the desired end results for whatever use is contemplated for the developed image. As will be understood, a variety of specific fixing techniques is available for use in connection with systems and methods and compositions embodying and for practicing this invention. Preferably, particularly in the cases where the developer agent is made up of dispersed droplets (an organosol) of resinsolvent solution (whether or not dyed or pigmented) in the non-polar vehicle, evaporation of the non-polar organic developer vehicle (preferably induced or aided by heating the developed sheet) is accompanied by similar evaporation of the solvent of the dispersed phase. If the resin developer agent of the dispersed phase in the non-polar vehicle organosol is selected. to have film-forming or binding properties upon evaporation therefrom of the polar solvent of the dispersedphase, a firm binding resin film is conveniently produced in the single. vehicle-solvent evaporation step.

Similarly, if the developer agent is a fusible pigment, fixing of the developer material to the image surface is satisfactorily achieved by fusing the developer agent on to the surface. Particularly in those instances where a colorless resin is including in the dispersed phase of the developer material and is dyed or pigmented by a dye or pigment soluble or dispersed therein, the resin may be satisfactorily selected to be a film-forming binder which, either by virtue of evaporation of the solvent or by the subsequent application of heat, will form a binding film medium for affixing a pigment dispersed therein to the image surface and/or a permanently adhered resin film dyed satisfactorily with the dye therein.

It should be understood that the foreoging includes, particularly with the utilization of pre-forme-d pigmentbinder-solvent systems dispersed in the non-polar developer vehicle, the fixing or drying of the pigmented or dyed developer agent as by oxidation of an oxidizable binder therein as well as by the fixing to the image surface of the pigmented or other composition by fusion from heat or by the evaporation of solvent therefrom as with a lacquer-type ink. Also, according to this invention, a pigment or resin or other developer agent may be fixed to the image surface by a substance applied thereto after the developer vehicle is removed by evaporation, or otherwise. For example, a dry, insoluble, and n=on-fusible pigment suspended in an appropriate non-polar developer vehicle may satisfactorily be fixed by the spraying thereover after drying of the vehicle of a solution of film forming resin which will tend, once applied, to bind the electrostatically deposited pigment into position. Similarly, the after-application of a suitable solvent may be utilized to dissolve or soften or otherwise form into a binder consistency or condition an electrostatically deposited resinous material. Particularly with situations where a dye or solution of a dye is electrostatically deposited in droplets or in particles overthe image as a developing agent, the resultant image may be satisfactorily fixed by the spraying thereover of a material which will solubilize the dye and/or the covered areas of the image film itself to enable the dye permanently to discolor or otherwise dye or atfix itself to the designated areas of the image surface to which it was electrostatically attracted. Also the image surface itself may be selected to contain a component which may be softened (but not sufficiently to distort or dissolve off or disrupt the image) by the non-polar vehicle, by the solvent of the dispersed phase, by a solvent applied after deposition, or by 'heat so that the deposited developer particles become affixed to the softened surface upon hardening thereof.

In any case, however, the particular solubility, thermoplastic, film-forming, and binding characteristics of the various materials, as explained above, are utilized to provide a variety of materials for the permanent fixing of developer agents to the image surface depending upon, among other factors, the particular material selected for the developing agent, :the particular end results or conditions desired from the developed image, and the other noted appropriate characteristics for the achieving of satisfactory results in the substantially permanent fixing to the image surface of the various developer agents and developer materials systems embodying and for practicing this invention.

-A further advantage or feature of control, particularly adapted to liquid development techniques, in electrophotographic reproduction methods or systems of the character to which this invention relates has also been discovered and will be explained in connection with the use of a counter-electrode for intensifying and controlling the electrostatic precipitation of developer agent from liquid developer compositions embodying and for practicing this invention and with particular respect to the conductive base 10.

9 purely diagrammatic illustrations in the accompanying drawing.

In the drawing:

FIG. 1 is an essentially diagrammatic showing of a cross section through an exposed image surface having an electrostatic charged image thereon;

FIG. 2 is an essentially diagrammatic showing of the image and charged surface of FIG. 1 with a counterelectrode in place thereabove in accordance with this invention;

FIG. 3 is a purely diagrammatic representation of a development result using developers in accordance with and for practicing this invention without the added effect of a counter-electrode;

FIG. 4 is a purely diagrammatic representation of the same result of FIG. 3 but depicting the effect achieved by a counter-electrode;

FIG. 5 is an exploded and somewhat diagrammatic view of one form of a counter-electrode embodying and for practicing this invention;

FIG. 6 is a diagrammatic showing of the counterelectrode plates of exploded FIG. 5 in operative position during the development of an image surface according to the teachings embodying and for practicing this invention;

FIG. 7 illustrates a counter-electrode brush for use in accordance with this invention as being formed of a mass of iron filings magnetically attracted to one end of a bar magnet;

FIG. 8 is a diagrammatic representation of apparatus for the continuous electrophotographic reproduction of an image on a web of paper or the like having an electrophotosensitive surface, with the image being projected onto the web; and

FIG. 9 is a diagrammatic representation of another.

embodiment of apparatus for electrophotographic reproduction of images on a continuous web, with the electrosheet or plate or other image carrier with the latent electrostatic image thereon, but drawn to no particular scale. In the diagram of FIG. 1, the plate or image carrier is indicated at 10, and may be considered as being either a sheet of paper or a metal plate. Later reference to the sheet or plate 10 as being electroconductive should be understood as being applied to either an actual metal plate or a piece of paper. That is, with the critical resistivities of the order of magnitude involved in electrophotography and with the conductivities involved as being of such orders of magnitude as are inherent with electrostatic images, the normal 6-10% residual moisture content of a sheet of paper renders that sheet of paper as a relatively good conductor, at least in terms of resistivities in the range of 10 or 10 ohm-centimeters.

On the base support 10 in FIG. 1 is shown a surface layer 11 of electrophotosensitive material having a charge image produced on the upper surface thereof. In the diagram of FIG. 1 (also FIG. 2) such charge image is illustrated by the minus signs in the areas 12, 13, and

14 as a schematic or diagrammatic means for indicating the discontinuous areas on the surface of image layer 11 carrying a negative electrostatic charge. In this particular illustration, the electrostatic charge carried by areas 12-14 is a negative charge, and, of course, produces corresponding positive charge accumulations 15, 16, and 17 indicated by the positive signs at the upper surface of base 10 adjacent to interface between the electrically insulating photoconductive layer 11 and the With the accumulation of electrostatic charges'in the areas 12-14 on the upper surface of image film 11, and

with, of course, the accumulation of oppositely charged areas 15- 17 at the upper surface ofbase'10, the electrostatic picture is complete. As is well known, however, the accumulation of these oppositely polarized charges at points spaced apart by the non-conductive electrophotosensitive image layer 11, an electric field is produced between the negative charges on the surface of layer 11 in areas 1214 and the positive charge accumulations at the top area of base It), and such field is indicated generally by the lines of fiux 20 in the diagram of FIGS. 1 and 2.

As will be noted from this description, and particularly with regard to relatively large image areas 1213such as large black or dark areas in a photograph or drawing or other material being electrostatically producedthe lines of force 20 are apparent at the edges of charged areas 12-14 and, in a manner of speaking, accessible from the outside thereof, by contrast with the discharged areas 21, 22, 23, and 24 between the charged areas 12-14. Accordingly, a positively charged dispersed developer agent in an electrically insulating or non-conductive liquid medium flowing over the upper charged surface of layer 11 in FIG. 1 tends, first of all, to be preferentially attracted to the lines of force 29 depicting the electric field existing between the concentration of negative charges in areas 12-14 and the corresponding concentration of positive charges therebelow in areas 1517. Such elec tric field, however, is, in a manner of speaking, primarily noticeable to charge particles dispersed in a liquid flowing over the upper surface of layer 11 at the edge portions only of the charged areas 12-14, and particularly of the larger charged area 13. The existing electric field induced by the central portions of large areas such as 13 is directed essentially downward through layer 11 and is not necessarily apparent to or effective upon the positively charged particles dispersed in a flow of developing material over the top of layer 11.

As a result, large dark or charged areas, such as 13 in FIG. 1, may be developed as diagrammatically depicted in FIG. 3 with the developer particles being most strongly or intensely precipitated or deposited upon or attracted to the charged area 13 only around the periphery thereof to produce an edge effect" by virtue of the fact that, regardless of the electrostatic charge in the area 13, the electric field set up between a concentration of negative charges on the upper surface of layer 1 1 and a corresponding concentration of positive charges at the upper surface of the conducting base 10 produces an attraction or intense concentration of development particle'sonly at the edges or periphery of the charged area 13.

It has been found, in accordance with this invention, that an increased uniformity and/ or intensification of developer particle deposition on, particularly, the large areas of the charged image can be enhanced, if desired, and controlled by the interposition over the imaged surface of what, for convenience, will here be called a counterelectrode, as systematically or diagrammatically illustrated in FIG. 2. Thus, the diagram of FIG. 2 also depicts a base support and conductive sheet or plate or layer 10 over the surface of which is formed essentially electrically insulating photoconductive layer 11. As in the situation depicted in FIG. 1, photo exposure of the top. surface layer 11 results in negatively charged image areas 12 14 thereon, which are illustrated as depicting a concentration of negative charges in areas of varying slzes.

If one positions a counter-electrode (which, in its broadest sense, can be considered as any relatively electrical conducting medium, here indicated as merely a metal plate 25 or roll or other conducting surface positioned closely adjacent to the charged surface 11 and grounded to the base 10, for example, by a specific conductor 26 or through the body of the person conducting the development), a concentration of positive charges 27, 28, and 29 will be accumulated in areas of the counterelectrode 25 corresponding to the negatively charged areas 1244 on the upper surface of layer 11, which concentration of charges will set up an electric field, indicated by the lines of force 30, between the upper surface of layer 11 and the counter-electrode 25and, indeed, preferentially to the downwardly extending electric field depicted in FIG. 1, provided, however, that the highly conductive counter-electrode 25 is spaced closely adjacent to the charged surface 11.

By contrast to the situation illustrated in FIG. 1 where the liquid developer is flowed over charged surface 11 the electric field of which is downwardly extending to conducting base 10, with the use of a counter-electrode 25 as is illustrated in PEG. 2, the developer material is flowed over charged image surface 11 but through the electric field, as indicated by the lines of fiux 36, upwardly extending between surface 11 and counter-electrode 25, and the intensification of deposition or electrostatic attraction or effect on the positively charged particles in the liquid developer is intensified so that an area, such as 12, which would be developed without the counter-electrode as diagrammatically illustrated in FIG. 3, now is developed, under the counter-electrode situation and conditions depicted in FIG. 2, to have a more or less uniform intensity of development or deposition throughout the entire area thereof, as indicated in FIG. 4.

As illustrative of appropriate means or apparatus for accomplishing the aforementioned counter electrode effect, there is illustrated in the exploded diagram of FIG. apparatus in accordance with this invention as comprising a top metal plate 35 and a bottom metal plate 3 6 between which are'sandwiched during the development the plate or sheet or other image carrier 37 having the image to be developed. Spacing members 38 are provided to space upper and lower plates 35 and 36 apart by some small but distinct extend-preferably no more than a small fraction of an inch-and the image carrier 37 is deposited within the area defined by spacers 33 so as to contact bottom plate 36 but be spaced from upper plate 35. The liquid developer, then, is flowed across the upper surface of image carrier 37 and be tween such upper surface and the lower surface of upper plate 35. Spacers 38 are, as will be understood, preferably provided of a non-conducting medium, and upper and lower plates 35, 36 are connected with a conductor 26 (which may satisfactorily be, as noted, merely the hand of the operator).

As a further means of increasing the intensification of deposition of the developer particles by the use of this counter-electrode apparatus, a positive electrical potential may be superimposed between upper and lower plates 35 and 36, as indicated by the battery symbol 40 interposed in the conductor 26 therebetween, for controlling the deposition and electrostatic precipitation of positivel y charged developer agent particles or droplets from the liquid developer material flowing over image carrier 37 and beneath upper plate 35 and through the electric field therebetween.

Since, as noted, the foregoing counter-electrode effect is obtained, according to this invention, by the adjacent positioning of any conductive material grounded to the image carrier base and closely spaced above the' charged image surface 11, a variety of arrangements, other than the metal plates 35 and 36 give satisfactory results. For example, a rnetal brush to which the developer particles may be preliminarily electrostatically attracted may be satisfactorily utilized in this connection with the plate or sheet or image carrier surface being developed immersed in either a non-polar organic liquid vehicle or a liquid composition of such non-polar vehicle with the developer agent suspended therein. Some difficulty may be experienced in finding a metal brush of the required or desired optimum fineness, but satisfactory results are achieved using as such metal brush a brush formed, as noted in FIG. 7, by dipping a bar magnet 45 into iron filings so that the filings, being magnetically attracted to the bar magnet, form what might be called the bristles 46 of a brush, the bar magnet forming the handle, which can be used as a counter-electrode by simply brushing the surface of charged layer 11 to have the desired intensifying effect on the uniform deposition of developer particles on the surface, whether such particles originate as being electrostatically attracted to the bristles of the brush or whether they are merely dispersed in a liquid developing com position in which the plate 10 is immersed and in which the brushing occurs. Also, as noted in the copending application of Donald L. Fauser and Edwin R. Kolb, now US. Patent 3,155,531 executed and filed of even dates herewith, certain other advantages may be achieved by utilizing such a magnetic brush as a counter-electrode in liquid developer systems of the character to which this invention relates and, particularly, when the developer agent includes a magnetic material.

With particular regard to forming visible reproductions of drawings or pictures or written matter as in the graphic arts, electrophotography has many advantages stemming from, for example, the continuous tone or photographic clarity and definition obtainable, etc. The-liquid developer systems embodying and for practicing this invention also lend themselves particularly to the multiple reproduction of electrophotographic copies by enabling electrophotographic advantages of multiple copy reproduction at vintually printing press speeds. Reference to FIG. 8 indicates a diagrammatic showing of apparatus for the continuous multiple reproduction of image material by electrophotography to a continuous web of electrophotosensitive paper or the like particularly for graphic art reproduction in the manner of a printing press.

According to FIG. 8 a roll of paper or the like is indicated at 50 as representing a continuous web of paper or other suitable base material provided with a suitable electrophotosensitive surface layer. From roll 50, the web 51 is withdrawn for feeding through the machine, as,

for example, by passing over a tension brake roll 52. A

registration punch or similar device for controlling or metering the feed of web 51 in increments commensurate with the lineal dimension of whatever image is desired to be repeatedly reproduced on the electrophotosensitive surface of web 51 is indicated at 53 for cooperation with a web length measuring roll 54 for controlling the feeding of web 51, either incrementally or continuously, through the apparatus. A registration mark reader and impression counter is indicated at 55 as a further component of the web feed control elements of the apparatus.

In the apparatus illustrated in FIG. 8, the electrophotosensi'tive surface is on the inside surface of web 51 (ie., the lower surface of the horizontal portions of web 51) and this electrophotosensitive surface is given a uniform electrostatic charge by a corona charging unit indicated at through which the web passes. After leaving corona charging unit 60, the electrophotosensitive web with a uniform electrostatic charge thereon passes into the exposure area of the machine indicated at 61 where a light image 62 is projected onto the web as by a projector 63 having lens elements 64, and condensers 65 for a source of light 66 for projecting light image 62 from, for example, a photographic transparency indicated at 67. The projection of light image 62 onto the charged surface of web 51, of course, alters the uniform electrostatic charge thereon which was produced by corona charging unit 60, and produces on web 51 a latent electrostatic charge or pattern.

Immediately after exposure to this light image, web

51 passes over guide roll 69 and around driving capstan 'jection of an image on to the web as with FIG. 8.

13 tion. Still driven by driving capstan 70, the web 51 continues, over guide rolls 77 and 78, to contact a heated drying drum 80 around which web 51 travels for the drying removal of the liquid developer vehicle and other solvent evaporation or heat fusion for fixing the developer agent fir-mly onto the surface of the web, after which web 51 leaves the drying step over guide roll 81 and passes on to a sheeter or other subsequent operations. As noted in FIG. 8, a counter-electrode 85 is preferably provided in the developing tank 76, and is illustrated as a magnetic brush in the form of the rotating magnetic roller carrying about the periphery thereof bristles of iron filings magnetically attracted to the roller for the desired contact relationship with the image surface of web 51 as it passes beneath driving capstan 70 in the liquid developing composition 75 in developer tank 76.

Also, a hood 90 is' preferably provided around drying drum 80 with a suction vent 91 to aid in the evaporation and removal of the developer vehicle and any other solvents as Web 51 passes around drying drum 80.

Referring now to FIG. 9, another embodiment of apparatus according to this invention is diagrammatically illustrated for providing similar continuous multiple reproduction of image material on a continuous" web, but having the light exposure of the electrophotosensitive web made by contact with a transparency, instead of by pro- In this embodiment, a roll 50 of electrophotosensitive web 51 is provided from which the web 51 is withdrawn over tension break 52 and through registration punch 53, to be fed over measuring roll 54 andthrough reader and counter 55 to corona charging unit 60 where the electrophotosensitive surface of the web 51 is given a uniform electrostatic charge. From charging unit 60, web 51 is .led over guide roll 95 around exposure cylinder 100.

This exposure cylinder is fabricated of transparent material and carries around the periphery thereof a photographic transparency or other source of light image 103 in much the same manner as the impression cylinder of a lithographic press carries around the periphery thereof .the lithographic plate from which successive impressions are to be made. Substantially at the axis of cylinder 100 is a flash lamp or other source of light 101 so.that, with web 51 (the electrophotosensitive surface thereof being against cylinder 100) is carried around cylinder 100, light source 101 (either by flash exposure or otherwise) lights up to produce a light image on the surface of web 51 through the transparency 103 around cylinder 100.

After exposure on exposing cylinder 100, web 51, passing over guide roll 102, is led to developing tank 76 containing a liquid developing composition 75 and, after having passed over guide roll 69, is immersed in developing tank 76 by driving capstan 70, as described with regard to FIG. 8, and emerges therefrom over guide rolls 77 and 78 to contact a heated drying drum 80', preferably positioned in a hood 90 with suction vent 91, where drying removal of the developer vehicle and other solvent evaporation or heat fusion incident to the fixing of the developed image is accomplished. Also, a counterelectrode is provided in the apparatus of FIG. 9 as indicated at 105, and is in the form of a stationary magnetic brush, rather than the rotating roller 85 of the apparatus of FIG. 8.

As will be understood, with regard to both FIGS. 8 and 9, at least that portion of the web travel from corona charging unit 60 to the emergence of the developed web or the charge image thereon is not exposed to light until development of the image, or, at least, exposed to no more than photographic darkroom safe light intensity or wave length of light.

.- As will be seen, with apparatus such as illustrated in FIGS. 8 and 9, continuous multi-reproductions can be a polyacrylic acid binder matrix.

14 made electrophotographically to utilize the photographic fineness and clarity and definition of an electrophotographic process and yet at speeds or quantities virtually approximating regular printing press speeds and, because of the liquid developer contributions according to this invention, Without the necessity of individual handling of each reproduction during development as well as avoiding the mechanical difliculties in a continuous operation of having the developer particles carried on a mechanical carrier and/or aerodynamically applied to the charge image during development.

As further illustrative of the operation and enhanced results achievable by liquid developer systems embodying and for practicing this invention, the following specific examples are, noted among those with which satisfactory results in the development of electrophotographic images according to this invention are obtained:

Example I A dispersion of black iron oxide pigment in Varnolene (a petroleum derivative indicated as number 3039 and supplied by the Sohio Oil Company) Was achieved by intimately admixing iron filings with a quantity of iron oxide pigment or powder (to break up agglomerations in the latter), and then pouring the filing-oxide mixture into Varnolene, as a result of which charged iron oxide particles floated off into a dispersion in which the de velopment was conducted. Fixing was accomplished by overcoating the developed image, after evaporation of the Varnolene vehicle by forced air drying, with a water solution of polyacrylic acid which was then dried to a,

firm transparent film.

Example II Finely ground Epon resin (as commercially available from the Shell Oil Company) was dispersed in Varnolene, in which Epon resin is not soluble, and an electrostatic image was developed on an electrophotographic surface comprising zinc oxide as a photoconductor dispersed in The developed image was fixed by heat fusion of the deposited resin on the plate surface during heat drying and evaporation of the developer vehicle. In this example, since it Was desired to emphasize the visible characteristics of the developed image, the intensity and contrast of the image were increased by the lithographic application of an ink. That is, since the surface itself, in non-image areas thereof, has the inherent characteristic of being hydrophilic and since the Epon resin developed image has oleophylic surface characteristics, the required visible intensity was achieved by dampening the entire surface with Water and then rubbing a standard greasy lithographic ink thereover with a cotton swab, as a result of which treatment, the ink was repelled by the non-image or undeveloped areas and was received by the image areas on which was the oleophylic fused Epon resin film.

Example IV For an organosol-type liquid developer agent, one part by weight saran resin was dissolved in parts mesityl oxide. The organosol was attained by dispersing with stirring one part by weight of the foregoing solution into 20 parts Varnolene, and the electrostatic charge image was developed. After drying the developed plate, the resin image was heat fused for fixing, and the visible image contrast was increased by applying lithographic ink on the fused image as with the previous example.

Example V As illustrative of fixing the developer material to the plate by softening of the image film surface, a liquid developer was made by dispersing one part by volume of a standard commercial Gravure Red ink (identified as IPI-FG*12277) in 500 parts Varnolene. An electrostatic charge image was developed on a plate with this developer and the image surface air dried. The ink pigment image was fixed onto the image surface by dipping the developed plate in toluene, a solvent for the binder component of the image surface (in this case an acrylic acid ester polymer known as Acryloid B-7 sold by Rohm & Haas) so that the image surface resin was softened sufiiciently to bind or adhere and permanently fix the ink pigment.

Example VII Using the same liquid developer as in the previous example, an electrostatic charge image was developed on a plate having as the binder component in the electrophotographic surface a methyl acrylic acid vinyl acetate copolymer (commercially available Elvalan resin) instead of the acrylic acid ester of the previous example. After the image was developed and air dried for removal of the Varnolene, the developer material was observed to be fixed onto the image surface. Since Varnolene is not a solvent for the image surface resin, fixing in this case was obtained by the action of the ink solvent and/or resin on the image surface film.

Example VIII The charge image on a plate similar to that in the previous example (i.e., with an Elvalan resin binder in the electrophotosensitive surface) was developed using the organosol dispersion of saran resin dissolved in mesityl oxide as in Example IV. When the developed plate was dried of the Varnolene vehicle, the image was observed to be fixed on the plate through the action of the mesityl oxide resin solvent with the Elvalan resin in the image surface binder.

With regard to the foregoing specifically illustrative examples, it should be noted that the electrophotosensitive surfaces referred to were utilized on both metal and paper bases or image carriers and comprises, as photoconductive material, finely divided zinc oxide dispersed in a variety of resin binding materials, all insoluble in non-polar organic solvents-cg, polyacrylic acid, methylacrylic acid vinyl acetate copolymer (Elvalan), acrylic acid esters (Acryloid B-7), etc. Charging of the electrophotosensitive coatings or surfaces prior to exposure to a light image was accomplished by a corona charging unit with a negative electrostatic charge being impressed on the image surface during sensitization thereof. Exposure to the light image was accomplished both by contact and projection types of exposure through photographic transparencies. The liquid development of the latent electrostatic image was accomplished by immersg the xpo ed P or image carrier in the developer if liquid as well as by pouring the developer liquid over the exposed plate. In either case, excess developer liquid, including excess dispersed developer material which might be merely gravitationally or mechanically deposited without attraction on the surface, was rinsed off the developed surface with clean non-polar solvent. Forced or normal air drying of the developed image was used for evaporating the residual non-polar vehicle, with or without heat for fusing the developer material in the fixing step as noted. In those examples where fixing was obtained by the after-application of a transparent overcoating to bind the deposited developer material pigment to the dried plate, either water soluble film formers (e.g., polyacrylic acid) or organic soluble film formers (e.g., parafiin or Epon in an appropriate solvent which has no disruptive or distortive solvent reaction with the binder component of the image surface) were satisfactorily used. Satisfactory results are also obtained by utilizing in the organosol-type of developer referred to in Example IV and related examples instead of the solution of saran resin in mesityl oxide as the dispersed phase, such other resin solutions as a commercial resin made by Eastman Kodak and designated as Kodak Photo Resist dissolved in a solvent therefor (KPR thinner), Epon resin in isopropenyl acetate, polyisopropenyl acetate in isopropenyl acetate, and Epon resin in mesityl oxide, etc., as noted.

It will, accordingly, be seen that liquid developers of various types are provided according to this invention for the development of a variety of different electrostatic charge images on a variety of different electrophotosensitive surface films or layers applied to a variety of different bases or plates or image carrier materials, and that, as the film characteristics of the electrophotosensitive surface may vary and as the ultimate end results of the developed image may vary, still the liquid development systems are provided, according to this invention, for the accomplishment and developing and fixing of a wide variety of electrostatic charge images applied to a wide variety of electrophotosensitive surfaces for a wide variety of ultimate end results. Similarly, system and methods and apparatus are also provided for controlling or intensifying, by a counter-electrode technique, of the actual development results experienced, including, of course, the added control that, by using a counter-electrode at the proper polarity and electric potential, one may not only provide the enhanced intensity and control of deposition of developer particles or droplets, but may also actually obtain or produce a positive or reversal print for a given developer of a given polarity with respect to a given charge image of a given polarity, merely by controlling the electric field force and polarity of the counter-electrode to conform to or be correlated with the force and polarity of the electrostatic charge image and, by selection according tothis invention, the polarity and attractive capacity of the charged developer particles.

As will be noted from the foregoing, the liquid development systems according to this invention contemplate both direct and reversal development of electrostatic images. Thus, if the electrostatic charge image to be developed is negatively charged and the developer material is positively charged, as indicated with the discussion of, for example, FIGS. 1 and 2, a direct development occurs with the developer material being attracted to the charged areas ofthe image. If, however, the charge image is negative and a negatively charged developer is used, deposition of the developer material, due to the repulsion thereof by the charge image, occurs on uncharged areas of the image surface to produce, in essence, a reversal development of the image. As also will be understood from the foregoing, such a situation is substantially facilitated by the utilization of a counterelectrode adequately charged to the correct polarity to provide in the developer flow area above the charged image surface an electrostatic field for controlling and intensifying precipitation or deposition of developer parof the operator. For example, a selenium image surface can satisfactorily be charged with either a positive or a negative charge prior to exposure, as can an electrophotosensitive surface comprising zinc sulfide as a photoconductor in an acrylic resin binder, whereas electrophotosensitive films utilizing zinc oxide as a photoconductor in a resin binder primarily take on a negative charge.

Considering the impressing of a potential between counter-electrode plates 35 and 36 (FIG. 6), it should be noted that a battery connection providing a polarity on upper plate 35 opposite to that of the charge image produces an intensification of deposition of developer particles, perhaps even including some unwanted deposition in non-image or background areas, and is particularly effective for the reproduction of images having large solid charge areas and/ or continuous tone images, and the like. In the development of screened half tones, and other types of material where maximum contrast is desired and the image is made up of relatively small solid areas, arranging the polarity of bottom plate 36 to be opposite to that of the charge image minimizes inadvertent deposition of developer particles in background areas without interfering with the desired-deposition on image areas.

While the methods, compositions and forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods, compositions and forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In an electrophotographic process of the character described in which an electrostatic charge image is produced on an electrophotographic surface, the developing steps which comprise treating said surface with an electrostatic charge image thereon with a liquid developer of two substantially immiscible phases at least the continuous phase comprising a liquid of high electrical resistivity, the dispersed phase forming a developer agent and comprising a resin dissolved in a solvent and carrying an electrostatic charge, said solvent being immiscible with said continuous phase, maintaining said surface in contact with said liquid developer for development of said charge image, and effecting substantially permanent adhesion of the developed image on said surface by removing said liquid of high electrical resistivity and the solvent for the dissolved resin.

2. A process as set forth in claim 1 wherein said developer agent includes a toning element, and wherein said surface is maintained in Contact with said developer for a period of time sufficient to cause deposition of toning elements as controlled by the latent image.

3. A process as set forth in claim 2 wherein said toning element is a pigment.

4. A process as set forth in claim 2 wherein said toning element is a dye.

5. A process as set forth in claim 2 wherein said toning element is dissolved coloring material.

6. A process as set forth in claim 1 wherein said dispersed phase comprises finely divided developer agent 18 dispersed in said liquid of high electrical resistivity as an emulsified phase, said developer agent including a resin in an amount sufiicient to form an emulsified phase, and wherein said surface is immersed below the level of liquid developer for a period of time sufiicient to cause deposition of said developer agent.

7. A process as set forth in claim 1 wherein said electrophotographic surface includes an organic polymeric binder, said solvent for said resin being a solvent for said binder for softening said surface, and drying the developed image for removal of said liquid of high electrical resistivity and said solvent for hardening said softened binder and substantially permanently affixing thereto the developer agent deposited on said surface.

8. A process as set forth in claim 1 wherein said liquid of high electrical resistivity is a non-polar liquid vehicle, and said resin being insoluble in said non-polar liquid vehicle and dissolved in a polar solvent miscible with said non-polar vehicle.

9. A process as set forth in claim 1 wherein said electrophotographic surface includes an organic polymer polar binder, said liquid of high electrical resistivity being nonpolar, and said solvent being polar.

References Cited by the Examiner UNITED STATES PATENTS 2,053,494 9/1936 Pirie et al. 117- --39 2,297,691 10/ 1942 Carlson.

2,638,416 5/1953 Walkup 252-62.1 2,703,280 3/1955 Butterfield et al. -1.7 2,753,308 7/ 1956 Landrigan 25262.1 2,776,907 1/ 1957 Carlson 117-21 X 2,784,694 3/1957 Crumrine et al 118-637 2,786,439 3/1957 Young 1l8-637 2,803,177 8/1957 Lowrie 951.7 2,811,465 10/1957 Greig 117-17.5 2,824,545 2/1958 Ricker 118637 2,854,947 10/1958 Giaimo 117-17.5 X 2,857,271 10/1958 Sugarman 117-17.5 X 2,862,815 12/1958 Sugarman et al 11717.5 2,877,133 3/1959 Mayer 118-637 X 2,884,704 5/1959 Bolton 117-21 X 2,890,968 6/1959 Giairno 118637 X 2,891,911 6/1959 Mayer et a1 25262.1 2,899,335 8/1959 Straughan 2 11737 2,907,674 10/ 1959 Metcalfe et al. 11737 2,913,353 11/1959 Mayer et al. 117--37 2,940,847 6/1960 Kaprelian 117-17.5 X 3,010,842 11/1961 Ricker 252-624 3,043,684 7/1962 Mayer 11717.5 3,155,531 11/1964 Fauser et al. 11737 3,241,957 3/1966 Fauser et a1. 961

FOREIGN PATENTS 755,486 8/ 1956 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

E. E. FULLER, RICHARD D. NEVIUS, JOSEPH B.

SPENCER, Examiners.

N. ANSI-1BR, M. SOFOCLEOUS, E. CABIC,

Assistant Examiners. 

1. IN AN ELECTROPHOTOGRAPHIC PROCESS OF THE CHARACTER DESCRIBED IN WHICH AN ELECTROSTATIC CHARGE IMAGE IS PRODUCED ON AN ELECTROPHOTOGRAPHIC SURFACE, THE DEVELOPING STEPS WHICH COMPRISE TREATING SAID SURFACE WITH AN ELECTROSTATIC CHARGE IMAGE THEREON WITH A LIQUID DEVELOPER OF TWO SUBSTANTIALLY IMMISCIBLE PHASES AT LEAST THE CONTINUOUS PHASE COMPRISING A LIQUID OF HIGH ELECTRICAL RESISTIVITY, THE DISPERSED PHASE FORMING A DEVELOPER AGENT AND COMPRISING A RESIN DISSOLVED IN A SOLVENT AND CARRYING AN ELECTROSTATIC CHARGE, SAID SOLVENT BEING IMMISCIBLE WITH SAID CONTINUOUS PHASE, MAINTAINING SAID SURFACE IN CONTACT WITH SAID LIQUID DEVELOPER FOR DEVELOPMENT OF SAID CHARGE IMAGE, AND EFFECTING SUBSTANTIALLY PERMANENT ADHESION OF THE DEVELOPED IMAGE ON SAID SURFACE BY REMOVING SAID LIQUID OF HIGH ELECTRICAL RESISTIVITY AND THE SOLVENT FOR THE DISSOLVED RESIN. 